Photomask and thin-film transistor fabricated using the photomask

ABSTRACT

A photomask includes; a source electrode pattern including; a first electrode portion which extends in a first direction, a second electrode portion which extends in the first direction and is substantially parallel to the first electrode portion, and a third electrode portion which extends from a first end of the first electrode portion to a first end of the second electrode portion and is rounded with a first curvature, a drain electrode pattern which extends in the first direction and is disposed between the first electrode portion and the second electrode portion, wherein an end of the drain electrode pattern is rounded to correspond to the third electrode portion; and a channel region pattern which is disposed between the source electrode pattern and the drain electrode pattern, wherein a center location of the first curvature and a center location of the rounded portion of the end of the drain electrode pattern are the same.

This application is a divisional of U.S. patent application Ser. No.12/978,446, filed on Dec. 24, 2010, which claims priority to KoreanPatent Application No. 10-2009-0131175, filed on Dec. 24, 2009, and allthe benefits accruing therefrom under 35 U.S.C. §119, the content ofwhich in its entirety is herein incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention relates to a photomaskand a thin film transistor fabricated using the photomask.

2. Description of the Related Art

Liquid crystal displays (“LCDs”) are one of the most widely used typesof flat panel displays. Generally, an LCD includes a pair of substrateshaving electrodes disposed thereon and a liquid crystal layer interposedbetween the substrates. In the typical LCD, thin-film transistors(“TFTs”) disposed on the substrates are driven to apply voltages to theelectrodes. Accordingly, orientations of liquid crystal molecules of theliquid crystal layer are rearranged, and thus the amount of light thatpasses through the liquid crystal layer may be adjusted according to theorientations of the liquid crystal molecules.

A source electrode, a drain electrode and a channel region of a TFT maybe formed by stacking a conductive layer and photoresist on a substrate,forming a source electrode pattern, a drain electrode pattern and achannel region pattern on the photoresist using a photomask and thenetching the conductive layer using the photoresist pattern.

As LCDs become slimmer, a linewidth of a channel region of a TFT isincreasingly reduced. Thus, the occurrence of even a small processingdeviation during fabrication of a TFT may result in an increased numberof channel open defects or channel short defects.

These defects have a serious negative effect on the operation of a TFT,thereby adversely affecting the overall reliability of a display deviceutilizing the same, whether the display device is an LCD, an organiclight emitting diode (“OLED”) display, plasma display or other type ofdisplay device.

BRIEF SUMMARY OF THE INVENTION

Aspects of the present invention provide a photomask used to fabricate athin-film transistor (“TFT”) having reduced channel-related defects andthus enhanced reliability.

Aspects of the present invention also provide a TFT with enhancedreliability which is fabricated using the photomask.

However, aspects of the present invention are not restricted to the oneset forth herein. The above and other aspects of the present inventionwill become more apparent to one of ordinary skill in the art to whichthe present invention pertains by referencing the detailed descriptionof the present invention given below.

According to an exemplary embodiment of the present invention, t aphotomask includes; a source electrode pattern including; a firstelectrode portion which extends in a first direction, a second electrodeportion which extends in the first direction and is substantiallyparallel to the first electrode portion, and a third electrode portionwhich extends from a first end of the first electrode portion to a firstend of the second electrode portion and is rounded with a firstcurvature, a drain electrode pattern which extends in the firstdirection and is disposed between the first electrode portion and thesecond electrode portion, wherein an end of the drain electrode patternis rounded to correspond to the third electrode portion, and a channelregion pattern which is disposed between the source electrode patternand the drain electrode pattern, wherein a center location of the firstcurvature and a center location of the rounded portion of the end of thedrain electrode pattern are the same.

According to another exemplary embodiment of the present invention, aphotomask includes; a source electrode pattern which includes aplurality of source electrode segments, and a drain electrode patternwhich includes a plurality of drain electrode segments, wherein verticesof at least three of the source electrode segments contact a firstvirtual circle.

According to another exemplary embodiment of the present invention,there is provided a TFT including a source electrode, a drain electrodeand a channel region which are fabricated using the above describedphotomask.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and features of the present invention willbecome more apparent by describing in detail exemplary embodimentsthereof with reference to the attached drawings, in which:

FIG. 1 is a diagram illustrating a structure of a first exemplaryembodiment of a photomask according to the present invention;

FIGS. 2 through 3B are diagrams illustrating a light transmission effectof the first exemplary embodiment of a photomask according to thepresent invention;

FIG. 4 is a diagram illustrating a structure of a second exemplaryembodiment of a photomask according to the present invention;

FIG. 5 is a diagram illustrating a structure of a third exemplaryembodiment of a photomask according to the present invention;

FIG. 6 is an enlarged diagram of a region VI shown in FIG. 5;

FIG. 7 is an enlarged diagram of a region VII shown in FIG. 5; and

FIG. 8 is a diagram illustrating a structure of a first exemplaryembodiment of a thin-film transistor (“TFT”) according to the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The invention now will be described more fully hereinafter withreference to the accompanying drawings, in which embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to theembodiments set forth herein. Rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout.

In the present specification, a photomask may denote a mask used to forma predetermined pattern on a photoresist. Specifically, the photomaskmay denote a mask used to form a predetermined pattern on a photoresistwhich is stacked on a substrate.

Hereinafter, first exemplary embodiment of a photomask according to thepresent invention will be described with reference to FIGS. 1 through3B.

FIG. 1 is a diagram illustrating the structure of the first exemplaryembodiment of a photomask according to the present invention. FIGS. 2through 3B are diagrams for explaining the light transmission effect ofthe first exemplary embodiment of a photomask according to the presentinvention.

Referring to FIG. 1, the first exemplary embodiment of a photomask mayinclude a source electrode pattern 10, a drain electrode pattern 20 anda channel region pattern 30.

The source electrode pattern 10 may include a first electrode portion11, a second electrode portion 12 and a third electrode portion 13.

Specifically, the source electrode pattern 10 may include the firstelectrode portion 11 which extends primarily in a first direction (e.g.,a Y direction), the second electrode portion 12 which also extendsprimarily in the first direction (e.g., the Y direction) to besubstantially parallel to the first electrode portion 11, and the thirdelectrode portion 13 which extends from a first end of the firstelectrode portion 11 to a first end of the second electrode portion 12and is rounded having a first curvature. In other words, the sourceelectrode pattern 10 includes first and second electrode portions 11 and12 which form branches of the source electrode pattern and a curvedthird electrode portion 13 which connects the first and second electrodeportions 11 and 12.

The drain electrode pattern 20 may be disposed between the firstelectrode portion 11 and the second electrode portion 12. Specifically,the drain electrode pattern 20 may extend in the first direction to bedisposed between the first electrode portion 11 and the second electrodeportion 12. Here, in one exemplary embodiment a first end of the drainelectrode pattern 20 disposed between the first and second electrodeportions 11 and 12 may be rounded with a second curvature to match thethird electrode portion 13.

At least a part of a second end of the first electrode portion 11, whichis disposed substantially opposite to the first end of the firstelectrode portion 11, and at least part of a first side of the drainelectrode pattern 20 may be rounded with a third curvature. In addition,at least part of a second end of the second electrode portion 12, whichis disposed substantially opposite to the first end of the secondelectrode portion 12, and at least part of a second side of the drainelectrode pattern 20 may be rounded with a fourth curvature to match therounded portion of the first side of the drain electrode pattern 20. Inone exemplary embodiment, the second curvature may be equal to ordifferent from the fourth curvature and the first curvature may be equalto or different from the third curvature.

The channel region pattern 30 may be disposed between the sourceelectrode pattern 10 and the drain electrode pattern 20. Specifically, achannel region may be a region which is defined by boundaries of thesource electrode pattern 10 and the drain electrode pattern 20 and isinterposed between the source electrode pattern 10 and the drainelectrode pattern 20, and the channel region pattern 30 may be a patternfor forming the channel region. A width L1 of the channel region pattern30 as measured from the source electrode pattern 10 to a correspondinglocation on the drain electrode pattern 20 is constant throughout thechannel region.

The channel region pattern 30 may include entrance portions 32 and acentral portion 31.

Specifically, the entrance portions 32 may be portions of the channelregion pattern 30 which are formed by the second ends of the first andsecond electrode portions 11 and 12 and the first and second sides ofthe drain electrode pattern 20, respectively. In addition, the centralportion 31 may be a portion of the channel region pattern 30 which isformed by the third electrode portion 13 and the first end of the drainelectrode pattern 20.

As described above, the third electrode portion 13 and the first end ofthe drain electrode pattern 20 included in the first exemplaryembodiment of a photomask may be rounded to correspond to one another.Therefore, the width L1 of the channel region, that is, the distancebetween the source electrode pattern 10 and the drain electrode pattern20 at the central portion 31 of the channel region pattern 30 may remainunchanged.

Furthermore, the second end of the first electrode portion 11 and thefirst side of the drain electrode pattern 20 included in the firstexemplary embodiment of a photomask may be rounded to correspond to oneanother. Also, the second end of the second electrode portion 12 and thesecond side of the drain electrode pattern 20 may be rounded tocorrespond to one another. Therefore, the width L1 of the channelregion, that is, the distance between the source electrode pattern 10and the drain electrode pattern 20, at the entrance portions 32 of thechannel region pattern 30 may remain unchanged.

In the first exemplary embodiment of a photomask, the width L1 of thechannel region at the entrance portions 32 of the channel region pattern30 may be equal to that of the channel region at the central portion 31of the channel region pattern 30.

A thin-film transistor (“TFT”) fabricated using a photoresist patternwhich is formed using the first exemplary embodiment of a photomask mayhave fewer channel open or channel short defects than a TFT fabricatedusing a photomask in which a source electrode pattern and a drainelectrode pattern are not rounded. Accordingly, the TFT fabricated usingthe first exemplary embodiment of a photomask may have a higher degreeof reliability.

The above effects of the first exemplary embodiment of a photomask willnow be described in greater detail with reference to FIGS. 2 through 3B.FIG. 3A is a graph illustrating light transmittances measured at firstthrough fifth positions (1) through (5) in the channel region pattern 30of the first exemplary embodiment of a photomask of FIG. 2 in which thesource electrode pattern 10 and the drain electrode pattern 20 arerounded. FIG. 3B is a graph illustrating light transmittances measuredat positions, which correspond respectively to the first through fifthpositions (1) through (5), in a channel region pattern of a comparativephotomask (not shown) in which a source electrode pattern and a drainelectrode pattern are not rounded.

Referring to FIGS. 3A and 3B, the deviation in light transmittance wasreduced from approximately 2% in FIG. 3B to approximately 0.7% in FIG.3A. That is, a channel region with a more uniform width can be formedusing the photomask according to the first exemplary embodiment thanusing the photomask (not shown) in which the source electrode patternand the drain electrode pattern are not rounded. Accordingly, thechannel open defect or channel short defect of a TFT fabricated usingthe first exemplary embodiment of a photomask can be reduced.

Hereinafter, a second exemplary embodiment of a photomask according tothe present invention will be described with reference to FIG. 4. FIG. 4is a diagram illustrating a structure of the second exemplary embodimentof a photomask according to the present invention.

Referring to FIG. 4, the second exemplary embodiment of a photomask mayinclude a source electrode pattern 10, a drain electrode pattern 20, achannel region pattern 30 and a bar pattern 35.

Since the source electrode pattern 10, the drain electrode pattern 20and the channel region pattern 30 are substantially identical to thoseof the first exemplary embodiment of a photomask, a detailed descriptionthereof will be omitted. Instead, the bar pattern 35, which is the maindifference between the first and second exemplary embodiments of thephotomasks, will be described in detail.

As shown in FIG. 4, the bar pattern 35 may be disposed corresponding toeach of the entrance portions 32 of the channel region pattern 30. Inone exemplary embodiment, the bar pattern 35 may be shaped like arectangle which extends in a second direction (e.g., an X direction).However, exemplary embodiments of the shape of the bar pattern 35 is notlimited to the rectangular shape and may vary as desired. For example,alternative exemplary embodiments include configurations wherein the barpattern 35 may be trapezoidal, circular or have various other shapes.

A side of the bar pattern 35 may be aligned with the first side of afirst electrode portion 11, as shown in FIG. 4. A width W2 of the barpattern 35 (i.e., the distance between a side of the bar pattern 35 toan opposite side thereof) may be smaller than a width W1 of the firstelectrode portion 11 (i.e., the distance between a side of the firstelectrode portion 11 and an opposite side thereof). In addition, adistance L3 between a side of the bar pattern 35 and a side of the drainelectrode pattern 20 may be smaller than the distance L1 between thesource electrode pattern 10 and the drain electrode pattern 20 at eachof the entrance portions 32 of the channel region pattern 30. Also, adistance L2 between a side of the bar pattern 35 and the first side ofthe first electrode portion 11 of the source electrode pattern 10 may besmaller than the distance L1 between the source electrode pattern 10 andthe drain electrode pattern 20 at each of the entrance portions 32 ofthe channel region pattern 30.

After a photoresist pattern is formed using the second exemplaryembodiment of a photomask which further includes the bar pattern 35, ifa TFT is fabricated using the photoresist pattern, the channel opendefect or channel short defect of the TFT can further be reduced. As aresult, the reliability of the TFT can further be enhanced.

Hereinafter, a third exemplary embodiment of a photomask according tothe present invention will be described with reference to FIGS. 5through 7.

FIG. 5 is a diagram illustrating a structure of the third exemplaryembodiment of a photomask according to the present invention. FIG. 6 isan enlarged diagram of a region VI shown in FIG. 5. FIG. 7 is anenlarged diagram of a region VII shown in FIG. 5.

Referring to FIG. 5, the third exemplary embodiment of a photomask mayinclude a source electrode pattern 10, a drain electrode pattern 20 anda channel region pattern 30.

The source electrode pattern 10 may include a plurality of sourceelectrode segments 15. In the present exemplary embodiment, each of thesource electrode segments 15 may be a rectangle which extends in thesecond direction (e.g., an X direction). However, the present inventionis not limited thereto. In fact, another exemplary embodiment includes aconfiguration wherein each of the source electrode segments 15 may be arectangle which extends in the first direction (e.g., the Y direction)(not shown).

The drain electrode pattern 20 may include a plurality of drainelectrode segments 25. Each of the drain electrode segments 25 may be arectangle which extends in the second direction (e.g., the X direction).However, the present invention is not limited thereto. In fact, anotherexemplary embodiment includes a configuration wherein each of the drainelectrode segments 25 may be a rectangle which extends in the firstdirection (e.g., the Y direction) (not shown).

The length of the source electrode segments 15 in the first direction(e.g., the Y direction), also hereinafter referred to as a “height” ofthe source electrode segments 15, may be substantially equal to that ofthe drain electrode segments 25 as shown in FIG. 5. However, alternativeexemplary embodiments include configurations wherein the sourceelectrode segments 15 and the drain electrode segments 25 may havedifferent heights.

Three or more of the source electrode segments 15 may have edges whichcontact a first virtual circle 50. In addition, three or more of thedrain electrode segments 25 may have edges which contact a secondvirtual circle 40.

Specifically, referring to FIG. 6, an extension line connectingrespective vertices, also referred to as corners, of three or more ofthe source electrode segments 15 may be part of the first virtual circle50. In addition, an extension line connecting respective vertices ofthree or more of the drain electrode segments 15 may be part of thesecond virtual circle 40.

Referring back to FIG. 5, three or more of the source electrode segments15 may contact a third virtual circle 60. In addition, some of thesource electrode segments 15 may contact both of the first and thirdvirtual circles 50 and 60, depending on their arrangement. The firstvirtual circle 50, the second virtual circle 40, and the third virtualcircle 60 may be concentric circles whose centers are located at thesame position within the drain electrode pattern 20.

Three or more of the source electrode segments 15 may contact a fourthvirtual circle 70, and three or more of the drain electrode segments 25may contact a fifth virtual circle 80.

Specifically, referring to FIG. 7, an extension line connectingrespective vertices of three or more of the source electrode segments 15may be part of the fourth virtual circle 70. In addition, an extensionline connecting respective vertices of the three or more of the drainelectrode segments 15 may be part of the fifth virtual circle 80.

The fourth virtual circle 70 and the fifth virtual circle 80 may beconcentric circles whose centers are located at the same position withinthe source electrode pattern 10.

The channel region pattern 30 may be disposed between the sourceelectrode pattern 10 and the drain electrode pattern 20. As in the firstexemplary embodiment of a photomask, the channel region pattern 30included in the third exemplary embodiment of a photomask may includeentrance portions 32 and a central portion 31.

Similar to the first exemplary embodiment of a photomask, the presentthird exemplary embodiment of a photomask ensures fabrication of a morereliable TFT.

Hereinafter, a first exemplary embodiment of a TFT according to thepresent invention will be described with reference to FIG. 8. FIG. 8 isa diagram illustrating a structure of the first exemplary embodiment ofa TFT according to the present invention.

Referring to FIG. 8, the first exemplary embodiment of a TFT may includea source electrode 100, a drain electrode 120 and a channel region 110.

The source electrode 100 may branch off from data wiring 105 and may befabricated using any one of the above-described photomasks according tothe first through third exemplary embodiments of the present invention.

The drain electrode 120 and the channel region 110 may also befabricated using any one of the photomasks according to the firstthrough third exemplary embodiments of the present invention.

Specifically, a photoresist pattern may be formed using any one of thephotomasks according to the first through third exemplary embodiments,and a conductive layer may be etched using the photoresist pattern,thereby forming the source electrode 100, the drain electrode 120, andthe channel region 110.

As shown in FIG. 8, the source electrode 100 of the first exemplaryembodiment of a TFT may be U-shaped. Also, an end of the drain electrode120 may be curved to correspond to the U-shaped source electrode 100.

The first exemplary embodiment of a TFT according to the presentinvention may have reduced number of channel open or channel shortdefects and thus may also enhanced reliability.

While the present invention has been particularly shown and describedwith reference to exemplary embodiments thereof, it will be understoodby those of ordinary skill in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the present invention as defined by the following claims. Theexemplary embodiments should be considered in a descriptive sense onlyand not for purposes of limitation.

What is claimed is:
 1. A photomask comprising: a source electrodepattern which comprises a plurality of source electrode segments; and adrain electrode pattern which comprises a plurality of drain electrodesegments, wherein vertices of at least three of the plurality of sourceelectrode segments contact a first virtual circle.
 2. The photomask ofclaim 1, wherein a center of the first virtual circle is located withinthe drain electrode pattern.
 3. The photomask of claim 1, wherein atleast three vertices of the plurality of drain electrode segmentscontact a second virtual circle.
 4. The photomask of claim 3, whereinthe first virtual circle and the second virtual circle are concentriccircles.
 5. The photomask of claim 1, wherein each of the plurality ofsource electrode segments and the plurality of drain electrode segmentsis shaped like a rectangle which extends in a first direction.
 6. Thephotomask of claim 5, wherein a length of the plurality of sourceelectrode segments in a second direction substantially opposite to thefirst direction is substantially equal to that of the plurality of drainelectrode segments.
 7. The photomask of claim 1, wherein at least threevertices of the plurality of source electrode segments contact a secondvirtual circle.
 8. The photomask of claim 7, wherein the first virtualcircle and the second virtual circle are concentric circles.
 9. Thephotomask of claim 1, wherein at least three vertices of the pluralityof source electrode segments contact a second virtual circle.
 10. Thephotomask of claim 9, wherein at least three vertices of the pluralityof drain electrode segments contact a third virtual circle.
 11. Thephotomask of claim 10, wherein the second virtual circle and the thirdvirtual circle are concentric circles.